Giving Multiple Armatures One Parent
As Nathan said, it's better to have a single armature, which will be the main animation tool (avoid mixing bones animation with object animation).
Check if all bones of the four legs have unique names (rename them if necessary), then select all four armatures and press Ctrl J to join them into one.
Then create in edit mode a new &quot;center&quot; bone, select the first bone of every leg, shift select the center bone and press Ctrl P (keep offset).
In this way in pose mode moving the center bone will  result in moving all four legs.
Then you can parent the center mesh to the center bone selecting the mesh, shift select the armature, go to pose mode, select the center bone, press Ctrl P (bone option).